One example of a structure for reducing wind noise mounted on a vehicle is shown in Japanese Laid-Open Patent Application No. 9-2339.
As shown in FIG. 5, a vehicle is equipped with a roof spoiler 100 on a roof of the vehicle at a predetermined height along the width of the vehicle. The roof spoiler 100 has a structure for reducing wind noise. The roof spoiler 100 comprises two surfaces, which are an upper surface 100A and a lower surface 100B. A flow regulating means 102 is shaped at least on one of two surfaces (It is the lower surface in the case shown in FIG. 5.). The flow regulating means 102 regulates a direction of the air flow flowing along the surfaces of the roof spoiler 100 to a predetermined direction, so that two pressures or two velocities generated along the upper and lower surfaces 100A, 100B of the roof spoiler 100 are unbalanced at the place near the rear end portion 100C. By the advantage of this structure, the distance between the very front and the very rear of the roof spoiler 100 is not unnecessarily long. That is, the size of the roof spoiler 100 is restrained, and a Karman vortex of the air flow is reduced. Accordingly, a wind noise of the roof spoiler 100 is reduced.
In the structure for reducing wind noise shown in FIG. 5, however, the difference between two pressures or velocities of the upper and lower air flows along the roof spoiler 100 might not be sufficiently high, because the flow regulating means 102 is shaped at least on one of the upper and lower surfaces 100A and 100B. It might result in not sufficiently eliminating the Karman vortex, which is the cause of the wind noise. It means that the wind noise might not be reduced efficiently by the above-mentioned structure for reducing wind noise.